This invention relates to an engine system including a four cycle internal combustion engine having a second intake valve openable during a period overlapping an exhaust cycle and the subsequent intake cycle to permit the admission of compressed air to a combustion chamber, and more particularly to a control system for varying the amount of air to be admitted to the combustion chamber in response to the intake air flow.
One engine system is known in which an air fuel mixture is admitted to a combustion chamber by a first intake valve during an intake cycle and air is admitted to the combustion chamber by a second intake valve during the intake cycle to swirl around the cylinder axis to produce a stratified charge comprising an ignitable cloud in the proximity of the electrode of a spark plug.
In another known engine system, an air fuel mixture is admitted to a combustion chamber by a first intake valve to swirl around the cylinder axis during an intake cycle and air is admitted to the combustion chamber by a second intake valve during the intake cycle to swirl within a plane substantially parallel to the axial plane containing the cylinder axis therein to bring out fast stable combustion. In this engine, the second intake valve is so arranged as to direct a jet of air toward the electrode of a spark plug to scavenge the same.
Still another engine system is known in which an air fuel mixture is admitted to a combustion chamber by a first intake valve during an intake cycle to swirl around the cylinder axis in one direction and air is admitted to the combustion chamber by a second intake valve during the initial stage of the intake cycle to swirl around the cylinder axis but in the opposite direction to produce a stratified charge comprising an ignitable cloud in the proximity of the electrode of a spark plug.
In these engine systems described above, under idling or deceleration conditions when a great deal of residual gas exists within a combustion chamber, smooth engine operation could not be expected because the air-fuel ratio supplied to the engine is set lean and because of the existance of the great deal of residual gas within the combustion chamber under these conditions.
The admission of air in these engines is effected by a second intake valve and under atmospheric pressure, and no precise control of the amount of air to be admitted is effected which might lead to excessive deviation of the air-fuel ratio within the combustion chamber from a certain optimum range.
Another engine system is known in which air is admitted to a combustion chamber during the last stage of a compression cycle so as to prevent excessive rise in heat within the combustion chamber and the admission of air is again effected during the last stage of the subsequent exhaust cycle to absorb heat from an exhaust valve and the electrode of a spark plug. In this engine system a source of compressed air is used for the admission of air.
In another known engine system, the admission of air is effected during the last stage of an expansion or combustion cycle and the subsequent exhaust cycle for the purpose of promoting oxidation of HC and CO contained in the exhaust gases.
In any one of the engine systems described above however, the performance, in power output and fuel consumption, at full load operating condition of the engine is not sufficient, requiring further improvement.
It is proposed, in still another known engine system, to admit scavenging air to a combustion chamber during an exhaust cycle so as to expel the residual gas out of the combustion chamber. Although, in this engine system, the scavenging is carried out, it is impossible to lean out the air fuel mixture.